1. Field of the Invention
This invention relates to a multilayer type printed-wiring board provided with a checking coupon for measuring the characteristic impedance of the data transmission wire pattern arranged between a CPU module and a memory module.
2. Related Background Art
Electronic devices such as game machines for home use and mobile telephone sets typically comprises a printed-wiring board arranged in the cabinet thereof and a CPU (central processing unit) module and a main memory module are mounted there along with other modules. The CPU module and the memory module are connected to each other by a data transmission wire pattern arranged on the printed-wiring board.
Meanwhile, the data transmission wire pattern of a printed-wiring board have to be designed in such a way that the impedance of the wire pattern shows a value that corresponds to the impedance specified for the CPU module and the memory module mounted on the printed-wiring board so that the CPU and the memory may operate reliably on a stable basis.
However, some of the data transmission wire patterns of the printed-wiring boards shipped from manufacturing plants after the completion of the manufacturing process can show discrepancies between the design values and the actual values due to various reasons including the conditions for etching copper foils in the data transmission wire patterns to consequently give rise to an impedance greater or smaller than the design value. When the impedance does not agree with the design value, it is no longer possible to transmit exchange signals between the CPU module and the memory module.
In view of the above circumstances, it is therefore an object of the present invention to provide a novel multilayer type printed-wiring board adapted to measuring the impedance of the data transmission wire pattern on the manufacturing floor in an easy and simple fashion.
Another object of the present invention is to provide a multilayer type printed-wiring board comprising a pair of data transmission wire patterns arranged at the opposite sides of the inner layer substrate and adapted to measuring the impedances of the two data transmission wire patterns in a single measuring operation to improve the efficiency of the measurement process.
According to the invention, the above objects are achieved by providing a multilayer type printed-wiring board comprising;
a first insulating layer;
a data transmission wire pattern arranged on said first insulating layer and adapted to data transmission between a CPU module and a main memory module to be used for the CPU;
an impedance measuring wire pattern arranged on said first insulating layer in the layer same as that of said data transmission wire pattern with a predetermined clearance to any adjacent wiring pattern;
a second insulating layer arranged on said data transmission wire pattern and said impedance measuring wire pattern; and
land sections for signals arranged on said second insulating layer and electrically connected to said impedance measuring wire pattern arranged on said first insulating layer by way of a through hole so as to be held in contact with the signal terminal of the probe for measuring the impedance of said impedance measuring wire pattern and a GND (grounding) land section held in contact with the GND terminal of said probe;
said impedance measuring wire pattern having a pattern length not smaller than about 30 mm and a pattern width same as that of said data transmission wire pattern when using a TDR (time domain reflectometer) unit.
As pointed out above, the impedance measuring wire pattern, for measuring the impedance of the multilayer type printed-wiring board is arranged in the layer same as that of the data transmission wire pattern adapted to data transmission between the CPU module and the main memory module to be used for the CPU, for which a certain level of impedance have to be secured.
Preferably, the transmission frequency of said data transmission wire pattern of said multilayer type printed-wiring board is not less than 130 MHz so as to allow high speed data transmissions.
Preferably, the clearance between said impedance measuring wire pattern of said multilayer type printed-wiring board and any adjacent wiring pattern is not less that twice of the pattern width of said impedance measuring wire pattern so as not to have any interference of the adjacent wiring pattern.
Preferably, the wiring pattern arranged around the impedance measuring wire pattern of the multilayer type printed-wiring board is a GND pattern connected to said GND land section by way of a plurality of through holes so as to eliminate any inductance component.
Still preferably, when a plurality of data transmission wire patterns are arranged in different layers in said multilayer type printed-wiring board, a plurality of impedance measuring wire patterns are arranged in different layers in correspondence to the respective data transmission wire patterns and electrically connected to each other by way of through holes.
Thus, with a multilayer type printed-wiring board according to the invention, since an impedance measuring wire pattern is arranged in the layer of the data transmission wire pattern and the pattern width that affects the impedance of the device is made equal to that of the data transmission wire pattern so that the impedance of the data transmission wire pattern can be measured accurately by means of a method of measuring the impedance of a multilayer type printed-wiring board according to the invention. The impedance of a multilayer type printed-wiring board can be measured accurately by means of a TDR (time domain reflectometer) unit when the impedance measuring wire pattern has a pattern length not smaller than about 30 mm.